Neurophysiological mechanisms underlie visual pattern perception. Processes (attention, cognition, memory) with neural correlates that are difficult to delineate are involved. The aims are to identify and investigate nontrivial perceptual mechanisms based upon contour and context, and to develop integrative models (theory) permitting quantitative predictions. One approach confronts the perceptual system via geometrical perceptual anomalies, i.e., the characteristic errors committed. These perceptual errors are not restricted to the classical line drawings (so-called visual illusions) used in initially demonstrating them. Tracking by eye, judgments of collinearity, size and shape collinearity, size and shape judgments are systematically disturbed in the presence of adjacent and intersecting contours. These anomalies will be pursued, including an approximation to the task of the air controller, eye tracking under time and task stress. The second approach is concerned with how the perceptual system manages to perform so well (veridically) under everyday circumstances. Pattern discrimination of simple shapes will be the point of attack. Subjects will be intact humans, adults and children, tested by psychophysical procedures. Stimuli will primarily consist of luminous patterns in completely dark surrounds, or black outline stimuli in white surrounds with the visible border providing a frame of reference (context) for size, shape, or orientation.